Air conditioning systems of motor vehicles generally have a recirculating air flap for adjustment between a recirculating air operation having in-vehicle circulation and an external air operation having ventilation of external air into the passenger compartment and discharge of the internal air to the outside.
Gas sensors are sometimes used in vehicles for monitoring the external air to close the recirculating flap of the air conditioning system if an elevated pollutant concentration prevails outside the vehicle.
Furthermore, gas sensors are provided for monitoring the cabin air to check the carbon dioxide content, which is influenced on the one hand by of the respiratory activity of the occupants and on the other hand also by leaks of air conditioning systems having coolants containing carbon dioxide. The carbon dioxide concentrations resulting because of the respiratory activity are lower than those from a leak.
Conventional spectroscopic measuring principles are in particular used for gas sensors, in which an infrared radiation source such as a glow coil operated in the low-current range emits infrared radiation over a measuring distance, whose absorption of infrared radiation is subsequently ascertained in an infrared detector. Furthermore, other sensor types such as chemical sensors, semiconductor gas sensors, gas FETs, and others are also conventional. In gas sensors of this type, the limited service life and the high demand on the power supply are generally problematic.